Various analog-to-digital data converters and conversion techniques are available for converting electrical signals from an analog domain to a digital domain. In general, the process of analog-to-digital conversion includes sampling an analog signal and comparing the sampled analog signal to a threshold value. A binary result is recorded depending upon the result of the comparison. The process of comparing the sample to a threshold may be repeated a number of times with each successive comparison using a different threshold and residue of the sample. The number of iterations typically affects the noise level of any result as well as the resolution of the ultimate digital signal.
The successive approximation register (SAR) converter is one example of an analog-to-digital converter (ADC). The SAR ADC performs a binary search for the digital value that best corresponds to the voltage of an analog signal. In a SAR ADC, a voltage input is compared with one half of a voltage reference. If the voltage input is greater than one half of the voltage reference, a logic ‘1’ is stored in a register. Alternatively, if the voltage input is less than one half of the voltage reference, a logic ‘0’ is stored in the register. Next, if the previous comparison indicated that voltage input is greater than one half of the voltage reference, the voltage input is compared with three-quarters of the voltage reference. Again, where the comparison indicates a greater than condition, then a logic ‘1’ is stored in the register. In contrast, if the comparison indicates a less than condition, then a logic ‘0’ is stored in the register. Alternatively, if the previous comparison indicated that voltage input is less than one half of the voltage reference, then voltage input is compared with one quarter of the voltage reference. Again, if the comparison indicates a greater than condition, then a logic ‘1’ is stored in the register. In contrast, if the comparison indicates a less than condition, then a logic ‘0’ is stored in the register. This process is continued for lower order multiples of the voltage reference. As will be appreciated, the aforementioned process is capable of providing an ADC result with high resolution in a relatively small amount of time. In particular, only a single iteration can be used to produce each bit of resolution. For example, for a ten-bit resolution only ten iterations are required, and for twenty bits of resolution only twenty iterations are required.